You already worked out what the problem is, you just haven't realized it yet. For problems like this, where it's not really the cable or the setup, sometimes you just have to debug/troubleshoot stuff that only happens on your system. For troubleshooting, you have to methodically work your way backward through a system, to find what part introduces the fault. You can do scattershot/random tests, or just randomly replace components for fun, but that's not a good strategy because you may or may not randomly hit upon what the problem is.
You noted that it only happens during part of the day, and you also note here that it happens if you press on the tweeter. That's the answer right there. It's pressure sensitive. And it's the tweeter itself.
During the time of day, the car is presumably in the sun, and as it heats up, puts that pressure on the tweeter in the same way. As debugging, you could test the theory by parking the car in shade during that time and see if it still happens.
You've narrowed it down to the tweeter itself. It doesn't have anything to do with todd's cable or your other components it's a Tesla fault, and something people could hit even with the premium version where these are enabled. Tesla is not likely to fix this, because it's not the premium interior and thus not expected to work.
You can get hiss like this when a cable is pinched. No way to really know without disassembling the tweeter itself. When you say tweeter- the ones by the mirror are the actual tweeters, the round ones up top are high-mid range imaging speakers. If it's the one by the mirror, those are pretty easy to take apart for an inspection. The top speakers are quite a lot harder to get at.